The overall objectives of this program are to obtain information about: (1) Transport of folate compounds (including the cancer chemotherapeutic agent, Methotrexate) into mammalian cells; and (2) Mechanism of folate-dependent enzymes, including dihydrofolate reductase, folinase isomerase, and methionine synthetase. Projects to be undertaken include: (1) Examination of the components and mechanisms of the transport systems for folate compounds, pterins and adenine in L1210 cells and in rat hepatocytes. (b) Characterization of the dihydrofolate reductase from L1210 cells with respect to the nature and spatial relationship of the substrate-binding sites and with respect to the MTX-binding properties of naturally-occurring and synthetic multiple forms; (c) Purification of methionine synthetase, via affinity chromatography, from bovine liver and L1210 cells, and investigation of the synthesis of the holoform of this enzyme and its role (along with vitamin B12 and transcobalamin II) in the replication of L1210 cells; and (d) Extrapolation of information obtained from the above projects to model systems for cancer chemotherapy.